This application is based on Patent Application No. 11-316107 (1999) filed Nov. 5, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an IC card connector for electronic devices, such as cellular phones, telephones, PDAs (personal digital assistance), portable audio devices and cameras, and more specifically to a switch structure for detecting the position of a write-protect button of an IC card.
2. Description of the Related Art
Electronic devices, such as cellular phones, telephones, PDAs and digital cameras, accept IC cards incorporating a memory or control circuit, such as SIM (subscriber identity module) cards, MMCs (multimedia cards) and Smart Media (trade name), for a variety of expanded functions and for identification of the user.
The IC cards of this kind typically have some provisions for protecting information stored in the internal memory against being overwritten. They are also provided with a means of undoing the write protect function so that the user can write information into the card.
A variety of write protect methods have been proposed. Of these, a method using a write protect button that can be slid between two positions as in floppy disks is considered advantageous because of its capability of repetitive use and simple structure.
In this slide button method, a write protect button that can be slid between two positions is provided on the card side, and the electronic device accommodating the card has an electric circuit that protects the card from being written into when the button is situated at one position and, when it is at the other position, allows the card to be written into.
A sensor structure for detecting the position of the write protect button may include one using light. The optical method, however, has problems that a satisfactory detection accuracy cannot be expected as the card thickness and size become smaller and that the optical sensor may stand in the way for reducing the size and cost depending on where it is arranged.
FIG. 14A and FIG. 14B show a conventional construction of the write protect button position detector using a contact spring.
In this conventional construction, a switch structure consisting of a contact spring 100 with a contact portion 100a and a stationary contact strip 101 detects the presence or absence of the write protect button 102 that slides between two positions. In this switch structure, when the write protect button 102 is at one position, these contact elements 100, 101 are separated (FIG. 14A). When the write protect button 102 is at the other position, the contact elements 100, 101 are in contact (FIG. 14B).
In this switch structure, the displacement of the contact spring 100 depends basically on the height (thickness) of the button 102. Considering a play due to a difference between the width of a card accommodating portion of the connector and the width of the card, the amount of deflection of the contact spring 100 is the play subtracted from the thickness of the button 102. So, if the protect button is 0.6 mm high and the play is 0.3 mm, for example, the amount of deflection is 0.3 mm. Taking a parts tolerance and an assembly tolerance also into consideration in addition to the play, the deflection amount of the contact spring 100 may in the worst case be only about 0.1 mm.
In the above conventional switch structure, the two contact elements are made to contact each other by the displacement of only one contact element 100, so that the play and the assembly tolerance make it difficult to secure a sufficient relative displacement between the two contact elements, resulting in a poor contact between the contact elements 100 and 101 and giving rise to a problem of being unable to detect the protect button position correctly and stably.
The present invention has been accomplished under these circumstances to provide a switch structure of the card connector which can precisely and reliably detect the position of the write protect button by making sure that the contact elements can always perform reliable and stable contacting and parting actions even when various error factors occur.
In this invention, two cantilevered contact springs are used. The first contact spring is urged so that its engagement portion engages the recessed portion of the inserted card corresponding to one of the two slide positions of the write protect button and the second contact spring is urged so that its engagement portion engages the recessed portion of the inserted card corresponding to the other slide position of the write protect button.
Thus, in the switch structure of this invention, at whichever of the two slide positions the write protect button is set, the engagement portion of one contact spring engages the write protect button and the engagement portion of the other contact spring engages the recessed portion adjacent to the write protect button. Hence, even if there are plays and dimensional tolerances, these contact springs can always be displaced by an amount equal to the height of the write protect button whenever the write protect button is switched in position.
Further in the switch structure of this invention, because the two contact springs are brought into or out of contact with each other by using the raised portion corresponding to the write protect button and the recessed portion adjacent to the raised portion, the displacement directions of the two contact springs are opposite. That is, when the two contact springs are displaced toward each other, they contact; and when they are displaced away from each other, they disengage.
Therefore, in this invention the two contact springs are brought into or out of contact with each other by the relative displacement between them equal to two times the height of the write protect button. This enables a reliable contact and separation between the two contact springs even with small or ultra-small cards in which a sufficient button height cannot be secured.
This invention therefore allows the position of the write protect button to be detected accurately and reliably at all times, preventing an erroneous operation of writing data into a write-protected card.
In another embodiment of a card connector of this invention for removably holding a card having a write protect button, the write protect button having a predetermined height and being slidable between two positions in a recessed portion formed in an outer surface of the card; a switch structure comprising a first cantilevered contact spring urged so that an engagement portion of the first contact spring engages a part of the recessed portion of the inserted card corresponding to one slide position of the write protect button; and a second cantilevered contact spring extending along and in the same direction as the first contact spring and urged so that an engagement portion of the second contact spring engages an outer wall surface of the inserted card near the write protect button; wherein the slide position of the write protect button is detected based on displacements of the first and second contact springs toward or away from each other.
In this invention two cantilevered contact springs are used. The first contact spring is urged so that its engagement portion engages the recessed portion of the inserted card corresponding to one of the two slide positions of the write protect button and the second contact spring is urged so that its engagement portion engages the outer wall surface (e.g., card side wall) of the inserted card near the write protect button.
In the switch structure of this invention, at whichever of the two slide positions the write protect button is set, the engagement portion of the second contact spring always presses against the outer wall surface of the card near the write protect button, so that the second contact spring is positioned by the outer wall surface of the card taken as a reference. The first contact spring, on the other hand, is always displaced by an amount equal to the height of the write protect button according to the slide position of the button.
In this invention, because the two contact springs are brought into or out of contact with each other based on their positions on the card, if there are plays and dimensional tolerances, it is possible to always obtain a relative displacement between the two contact springs equal to the height of the write protect button.
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of embodiments thereof; taken in conjunction with the accompanying drawings.